The low costs associated with iron-based FT catalysts have heretofore been a major factor in the lack of development of methods for regenerating these catalysts. However, increasing concerns over disposal of industrial wastes in landfills from both economic and environmental standpoints have created a need for improved methods for recycling spent catalysts —even for the low-cost catalysts. When a catalyst is employed in a slurry reactor, disposal of spent catalyst can be challenging. Some methods have been proposed which rejuvenate iron-based catalysts for a short period of time, but an economical method is needed for returning the catalyst back to its initial oxide state without causing attrition or sintering of the catalyst.
Moreover, to regenerate such iron-based catalysts, several areas of concern must be addressed. The oxidation step must be controlled to prevent overheating and sintering of the catalyst. Usually, the temperature during oxidation is controlled by limiting the percentage of oxygen present in the gases used for oxidation. However, when limited oxygen is available during oxidation, the presence of wax with the catalyst can cause carbon formation. Therefore, efficient and complete wax removal is a key to successful catalyst regeneration. Further, de-waxing must be carried out in a continuous flow system without subjecting the catalyst to mechanical stresses, which can cause the catalyst particles to break apart.
The present invention provides an economical method of returning an iron-based FT catalyst back to its initial oxide state without causing catalyst attrition or sintering, thereby allowing the regeneration of a catalyst that has become deactivated due to buildup of contaminants on its surface.